1. Field of the Invention
The present invention relates to a static memory cell and, more particularly, to a static random access memory (referred to as an SRAM hereinafter) requiring no data refresh.
2. Description of the Related Art
In general, unlike a dynamic random access memory (DRAM) in which data is updated (refreshed) every predetermined period, a static memory requiring no data refresh can be easily used. In addition, when the static memory is combined with a CMOS technique, a random access memory backed up by a battery having a low standby power can be obtained. However, in this case, since a flip-flop must be formed in a memory cell, the cell area of the static random access memory is larger than that of the DRAM.
In an SRAM to which the present invention is not applied, since a CMOS structure must be independently formed in a memory cell, the cell area is six times or more than that of the DRAM.
According to another method, four transistors must be integrated in a cell, and an NMOSFET has a driving ability of several mA. Therefore, since the resistance of the ground power supply line of the cell must be decreased, a low-resistance wiring material such as polycide must be used, and difficult processing must be performed.